I guess rankings are cool now?
1: Gen V (More story-based, great post-game, and a ton of new, amazing Pokémon like Braviary, everything in the Desert Resort, Cinccino, and many more. Probably biased with this being my entry into the series....)
2: Gen III (Legends are incorporated into the story, a good post-game, and best champion Steven Stone. Salamence being in the dex is just a bonus)
3: Gen IV (Great new Pokémon like Lucario and Drapion, cool cross-gen evos like Electivire and Honchkrow, a good post-game, and brought competitive battling to a new level. Too bad DP were so slow, fixed with Plat.)
4: Gen VI (An amazing regional dex and brought the series to 3D! Hawlucha, Greninja, and Tyrantrum are fantastic new additions, among others. The story regressed a bit and the post-game is lackluster, but still a solid entry)
5: Gen I (Started it all, and I can't wait to revisit them without emulation! Also has best fire types Growlithe and Arcanine! Poor gameplay elements bog it down, glitched or intentional. Also, what post-game?)
6: Gen II (Too grind-y and too Kanto reliant. Has a lot of poor mons that only got upgrades later on/still suck. The remakes only slightly ease the pain. Not even Scizor, Heracross, and Feraligatr can save this)